Probe optical assemblies and probes for optical coherence tomography

ABSTRACT

Probes optical assemblies and probes for optical coherence tomography (OCT) applications are disclosed. The probe assembly includes an optical fiber, a stub lens and a light-deflecting member arranged in a cooperative optical relationship to define an optical path between the optical fiber end and an image plane that is folded by the light-deflecting member. The optical probe includes a transparent jacket that contains the optical probe assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______,entitled “Methods of making a stub lens element and assemblies usingsame for optical coherence tomography applications,” and to U.S. patentapplication Ser. No. ______, entitled “Stub lens assemblies for use inoptical coherence tomography,” both of which have been filed on the sameday as the present application and both of which are incorporated byreference herein.

FIELD

The present invention relates to optical coherence tomography, and inparticular to probe optical assemblies and probes for optical coherencetomography.

BACKGROUND ART

Optical coherence tomography (OCT) is used to capture a high-resolutioncross-sectional image of scattering biological tissues and is based onfiber-optic interferometry. The core of an OCT system is a Michelsoninterferometer, wherein a first optical fiber is used as a reference armand a second optical fiber is used as a sample arm. The sample armincludes the sample to be analyzed as well as a probe that includesoptical components. An upstream light source provides the imaging light.A photodetector is arranged in the optical path downstream of the sampleand reference arms.

Optical interference of light from the sample arm and the reference armis detected by the photodetector only when the optical path differencebetween the two arms is within the coherence length of the light fromthe light source. Depth information from the sample is acquired byaxially varying the optical path length of the reference arm anddetecting the interference between light from the reference arm andscattered light from the sample arm that originates from within thesample. A three-dimensional image is obtained by transversely scanningin two dimensions the optical path in the sample arm. The axialresolution of the process is determined by the coherence length.

To obtain a suitably high-resolution 3D image, the probe typically needsto meet a number of specific requirements, which can include:single-mode operation at a wavelength that can penetrate to a requireddepth in the sample; a sufficiently small image spot size; a workingdistance that allows the light beam from the probe to be focused on andwithin the sample; a depth of focus sufficient to obtain good imagesfrom within the sample; a high signal-to-noise ratio (SNR); and a foldedoptical path that directs the light in the sample arm to the sample.

In addition, the probe needs to fit within a catheter, which is thensnaked through blood vessels, intestinal tracks, esophageal tubes, andlike body cavities and channels. Thus, the probe needs to be as small aspossible while still providing robust optical performance. Furthermore,the probe operating parameters (spot size, working distance, etc.) willsubstantially differ depending on the type of sample to be measured andthe type of measurement to be made.

SUMMARY

An aspect of the disclosure is a probe optical assembly for a probe foran OCT system, wherein the assembly includes in order along an axis anoptical fiber having an end that defines an object plane, and a stublens element. The stub lens element has stub section with a proximal endthat resides adjacent the optical fiber end. The stub section is formedintegral with a lens and has a proximal end that includes a lenssurface. The assembly also has a light-deflecting member arrangedadjacent and spaced apart from the lens surface of the stub lenselement. The light-deflecting element has an axis that defines a workingdistance WD to an image plane. The optical fiber end, the stub lenselement and the light-deflecting member are arranged in a cooperativeoptical relationship to define an optical path between the object andimage planes that is folded by the light-deflecting member.

The disclosure also includes a probe for an optical coherence tomographysystem, wherein the probe includes a transparent jacket that containsthe probe optical assembly and through which the optical path passes.

Another aspect of the disclosure is a probe optical assembly thatdefines an optical path and that is suitable for use in forming an OCTprobe. The probe optical assembly includes a stub lens sub-assembly thatoperably supports i) an optical fiber having a first end and a secondend, and ii) a stub lens element having a central axis, a lens with alens surface that defines a distal end, and a stub section integrallyformed with the lens and having a proximal end, the stub lenssub-assembly being configured so that the optical fiber end is inoptical communication with the stub lens proximal end over the opticalpath. The probe optical assembly also has a support member configured tooperably support the stub lens sub-assembly so that the lens of the stublens element resides within the interior. The probe optical assemblyalso has a light-deflecting member having a second axis and operablysupported by the support member so that the first and second axes aregenerally coaxial. A portion of the second axis is folded to define afold in the optical path.

It is to be understood that both the foregoing general description andthe following Detailed Description represent embodiments of thedisclosure, and are intended to provide an overview or framework forunderstanding the nature and character of the disclosure as it isclaimed. The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated into andconstitute a part of this specification. The drawings illustrate variousembodiments of the disclosure and together with the description serve toexplain the principles and operations of the disclosure.

Additional features and advantages of the disclosure are set forth inthe detailed description that follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the disclosure as described herein, including the detaileddescription that follows, the claims, and the appended drawings.

The claims are incorporated into and constitute part of the DetailedDescription set forth below.

Any numerical provided herein are inclusive of the limits providedunless otherwise stated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a rod made of an optical material, shown withone of its ends operably arranged relative to a heat source;

FIG. 2 is similar to FIG. 1 and shows a stub lens element formed byheating one end of the rod to form a bulbous end portion that defines alens having a lens surface;

FIG. 3A is similar to FIG. 2 and shows the stub lens element in theprocess of having its lens reduced in size in the lateral dimension bymechanical means;

FIG. 3B is similar to FIG. 3A and shows the stub lens element having itslens reduced in size in the lateral dimension via laser processing witha laser beam;

FIG. 4A and FIG. 4B illustrate examples of the stub lens element formedby processing the lens to reduce its lateral dimension;

FIG. 4C is similar to FIG. 4B and shows an example where the lenssurface includes an anti-reflection coating;

FIG. 5A and FIG. 5B are similar to FIG. 4A, with FIG. 5A showing acutting tool being used to cut the stub section to form an angledproximal end, the resulting angled proximal end being shown in FIG. 5B;

FIG. 6A is a cross-sectional view of an example stub lens element shownalong with a cylindrical sleeve;

FIG. 6B is similar to FIG. 6A and shows the stub element operablyengaged with the sleeve to form a stub lens sub-assembly;

FIG. 6C is similar to FIG. 6B and shows an example sleeve that includesa slot that leads from the sleeve outer surface to the sleeve centralchannel;

FIG. 6D is similar to FIG. 6C and shows an adhesive material disposed inthe slot and that serves to secure the stub section of the stub lenselement to the sleeve;

FIG. 7A is similar to FIG. 6B and shows the stub lens sub-assembly ofFIG. 6A along with an example optical fiber ferrule;

FIG. 7B is a close-up view of the optical fiber ferrule of FIG. 7A;

FIG. 7C shows the optical fiber ferrule with an optical fiber securedtherein, engaged with the central channel of the sleeve to form a stublens assembly, and also shows a photodetector used to measure the modefield diameter of the focused light when performing alignment of thestub lens element relative to the optical fiber;

FIG. 8A is a cross-sectional view that shows the stub lens assembly anda light-deflecting member along with a support member in the form of anouter sleeve, in the process of fabricating a probe optical assembly tobe used to form an OCT probe;

FIG. 8B shows the stub lens assembly, light-deflecting member and outersleeve operably arranged to form the probe optical assembly;

FIG. 9A is a cross-sectional view of an example OCT probe that utilizesthe probe optical assembly of FIG. 8B;

FIG. 9B is a close-up view of the probe optical assembly containedwithin the interior of the jacket of probe, showing incident light andscattered light traversing the optical path in opposite directions;

FIG. 10 plots the object distance OD (horizontal axis) vs. the workingdistance WD (left vertical axis, solid-line curve) and the mode fielddiameter MFD (right vertical axis, dotted-line curve) in connection withdesigning an example stub lens element, with all dimensions being inmicrons;

FIG. 11 is a plot similar to that of FIG. 10 that plots the imageMFD_(IM) (microns) versus the working distance WD (microns) for the caseof a single-mode optical fiber, but where the fiber MFD_(F) is changedfrom 10 um to 7 um.

FIG. 12 is similar to FIG. 7B and illustrates an example modification ofthe optical fiber by providing a lens at the optical fiber end either byre-shaping the otherwise flat optical fiber end or by adding a separatelens element;

FIG. 13A through FIG. 13C illustrate an example method of forming afiber pigtail lens assembly using a fusion splicing process;

FIG. 13D is similar to FIG. 13C and shows the fiber pigtail assemblyoperably engaged with the ferrule so that the lens is adjacent one ofthe ferrule ends;

FIG. 13E is similar to FIG. 13D and shows an example embodiment wherethe lateral dimension of the lens has been reduced in size;

FIG. 13F shows the fiber pigtail assembly of FIG. 13E as arranged in aferrule, with the ferrule and fiber pigtail operably disposed on atransparent support substrate adjacent a light-deflecting member;

FIG. 14 is similar to FIG. 8B and illustrates an example embodiment ofthe probe optical assembly that employs a fiber pigtail lens assembly inplace of the stub lens assembly;

FIG. 15 is a plots the relationship between the length L (mm) of a stublens element and the lens diameter D2 (mm) of the stub lens element;

FIG. 16A is a cross-sectional view of another example embodiment of thestub lens assembly that includes the fiber pigtail lens assembly thathas a first fused fiber lens element in combination with a second stublens element;

FIG. 16B is similar to FIG. 16A, but with the outer sleeve replaced by asupport substrate;

FIG. 17 is similar to FIG. 16B and illustrates another exampleembodiment of a fused lens assembly wherein the support substrate ismade of a transparent material, and the second stub lens has an angledsurface that serves as a total-internal-reflection (TIR) mirror;

FIG. 18 is similar to FIG. 17 and illustrates an embodiment thatincludes a transparent monolithic structure that includes a stub lenselement portion;

FIG. 19 is a plot of the length L (microns) (horizontal axis) versus theimage MFD_(IM) (microns) (left-hand vertical axis) and working distanceWD (microns) (right-hand vertical axis) as defined as the beam-waistlocation, for an example fused lens element suitable for use in thefiber pigtail lens assembly;

FIG. 20 is a side view of an example fused fiber pigtail lens assemblywherein the lens includes an angled surface that defines a TIR mirrorthat serves to fold the lens axis and direct it through a portion of thelens surface; and

FIG. 21 is similar to FIG. 20 and illustrates another embodiment of thefiber pigtail assembly.

Additional features and advantages of the disclosure are set forth inthe Detailed Description that follows and will be apparent to thoseskilled in the art from the description or recognized by practicing thedisclosure as described herein, together with the claims and appendeddrawings. It will be understood that the illustrations are for thepurpose of describing particular embodiments and are not intended tolimit the disclosure or appended claims thereto. The drawings are notnecessarily to scale, and certain features and certain views of thedrawings may be shown exaggerated in scale or in schematic in theinterest of clarity and conciseness.

Cartesian coordinates are shown in certain of the Figures for the sakeof reference and are not intended as limiting with respect to directionor orientation.

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. Unless otherwise specified, a range of values, when recited,includes both the upper and lower limits of the range. As used herein,the indefinite articles “a,” “an,” and the corresponding definitearticle “the” mean “at least one” or “one or more,” unless otherwisespecified.

The mode field diameter MFD is a measure of the spot size or beam widthof light propagating in a single mode fiber. The mode field diameter MFDis a function of the source wavelength, fiber core radius r and fiberrefractive index profile. In an example, the mode field diameter MFD canbe measured as the full width at 13.5% of the peak power for a best fitGaussian beam, while in another example it can be measured by using thePeterman II method, where MFD=2 w, and

$w^{2} = {2\frac{\int_{0}^{\infty}{E^{2}r\ {r}}}{\int_{0}^{\infty}( {{E}/{r}} )^{2}}r{r}}$

wherein E is the electric field distribution in the optical fiber and ris the radius of the optical fiber core.

With reference to the Figures discussed in greater detail below, themode field diameter MFD is also referred to herein as a property of animage spot 652 formed at a working distance WD by a probe opticalassembly 450 and in this instance is referred to as the image mode fielddiameter MFD_(IM), or “image MFD_(IM)” for short, since the probeoptical assembly images an end 324 of an optical fiber 320, as explainedbelow. The mode field diameter MFD associated with optical fiber 320 isthus called the fiber mode field diameter MFD_(F), or “fiber MFD_(F)”for short. An example range for the working distance WD (see FIG. 9A) is5 mm≦WD≦15 mm. An example image MFD_(IM) is in the range of 15microns≦MFD_(IM)≦100 microns.

Stub Lens Element

FIG. 1 is a side view of a rod 10 made of an optical material. Exampleoptical materials for rod 10 include PYREX® glass, silica, VYCOR® glassor an optical glass. An example rod 10 has a cylindrical shape with anyone of a number of possible cross-sectional shapes, such as circular,elliptical, polygonal, etc. The rod 10 has a body 12 that defines acentral axis A1, a proximal end 14, a distal end 16, and across-sectional dimension (e.g., a diameter) D1. An example diameter D1for rod 10 is in the range of 250 microns and 1000 microns for acircular cross-sectional shape.

FIG. 1 also shows rod distal end 16 operably disposed relative to a heatsource 20. An example heat source 20 includes at least one heatingmember 21 that generates heat 22. An example heating member 21 includesan electrical arc, a laser, a joule-heating element, a flame, a ringburner, etc. The heat 22 is applied to a distal end portion 17 of rod 10adjacent distal end 16 while the rod is disposed vertically, i.e., withaxis A1 oriented in the direction of gravity. The heat 22 is sufficientto make the distal end portion 17 flow, whereupon surface tension causesthe distal end portion to become bulbous, as illustrated in FIG. 2.Depending on the cross section of rod 10 and processing conditions, theshape can be spherical, ellipsoid, etc. The now bulbous distal endportion 17 has a diameter D2, which in an example is in the range ofabout 300 microns to 2,500 microns. In an example, a rod 10 made ofsilica glass and having a diameter D1 of about 500 microns and having acircular cross-sectional shape allows for diameter D2 to be about 1.5mm.

The bulbous distal end portion 17 defines a lens 40 having a lenssurface 42. The size of lens 40 and the shape of lens surface 42 can becontrolled by controlling the rod-end melting process, e.g., bycontrolling at least one of: the amount of heat 22 provided by heatsource 20, the feed rate of rod 10 into heat 22, the rotation of the rodabout its central axis A1, and the distance over which the rod islowered into the heat. In particular, lens surface 42 can be madespherical to a high degree of accuracy using this process, thoughaspherical lens surface shapes can be made as well. In an example, wherelens surface 42 is spherical, it can have a radius of curvature R2 inthe range 0.15 mm≦R2≦1.5 mm (see FIG. 3A and FIG. 4A).

In an example, further processing is carried out to change the shape oflens 40, and in particular to reduce the lateral dimension of the lens.FIG. 3A is similar to FIG. 2, and illustrates an example embodimentwherein lens 40 is in the process of being reduced in size in thelateral dimension via mechanical grinding by a mechanical grinder 50.FIG. 3B is similar to FIG. 3A and illustrates another example of lens 40being reduced in size in the lateral dimension via laser processing by alaser beam LB. Arrows AR in FIG. 3A and FIG. 3B show the direction ofmotion of mechanical grinder 50 and laser beam LB, respectively.

FIG. 4A and FIG. 4B illustrate examples of a resultant stub lens element100 formed by processing lens 40 such that its lateral dimension isreduced. In one example, processed lens 40 has a reduced lateraldimension D2′ in the range about 600 microns to 1 mm, while in anotherexample the reduced lateral dimension D2′ is in the range 700 microns to800 microns. With reference to FIG. 4B, in an example, stub lens element100 has an axial length L from proximate end 14 to lens surface 42 thatis in the range 0.5 mm≦L≦5 mm.

The stub lens element 100 includes stub section 110 formed by theunaffected portion of rod 10 and the reduced-size lens 40, whichhereinafter is referred to as stub lens 40. The stub lens 40 has anon-lens outer surface portion 44 adjacent lens surface 42. The stubsection 110 serves as a handle for handling stub lens element 100 andcan be cut to have a length suited for its particular application. Thestub lens element 100 of FIG. 4A has a stub lens 40 with a conic orflared outer surface portion 44, while the stub lens of FIG. 4B has acylindrical outer surface portion. As shown in FIG. 4B, stub section 110has a length L1=L−2. (R2).

As illustrated in the example stub lens element 100 of FIG. 4A, theflared shape of lens 40 is employed to accommodate light 650 thatdiverges as it passes from proximal end 14 to distal end 16. The stublens 40 of FIG. 4A also shows a relatively short stub section 110 thatcan be formed by the aforementioned cutting after stub lens element 100is formed as described above. A transition portion 120 forms theconnection between stub section 110 and stub lens 40.

In examples, lens surface 42 of stub lens 40 can be spherical oraspherical. Example aspherical surfaces include bi-conic, parabolic,hyperbolic, etc. The shape of lens surface 42 can be defined bycontrolling the above-described melt process. In an example, ananti-reflection coating 46 can be applied to lens surface 42, asillustrated in FIG. 4C.

FIG. 5A is similar to FIG. 4A and shows a cutting tool 150 being used tocut stub section 110 of stub lens element 100 to form an angled proximalend 14 that defines an angle θ relative to axis A1, as shown in FIG. 5B.The angled proximal end 14 can serve to reduce back reflections whenstub lens element 100 is used in an OCT probe, as described in greaterdetail below. An example angle θ is in the range from about 5° to about12°.

OCT Probe Assemblies

Aspects of the disclosure are directed to OCT probes and assemblies usedin such probes. FIG. 6A is a cross-sectional view of an example stublens element 100 along with a cylindrical sleeve 200. The cylindricalsleeve 200 has a central axis A2, first and second ends 202 and 204, anouter surface 206, and a central channel 210 that runs along the centralaxis and that is open at the first and second ends. The central channel210 is sized to accommodate stub section 110 of stub lens element 100.The sleeve 200 can be made of any rigid material, with glass, plasticand metal being some exemplary materials. An exemplary sleeve 200comprises a section of precision capillary tubing, which can be drawndown to a select size from a much larger tube using a process similar toa redraw process used to make optical fibers. As sleeve 200 is laterincorporated into another larger sleeve as is explained below, it isreferred to hereinafter as inner sleeve 200.

FIG. 6B is similar to FIG. 6A and shows stub lens element 100 engagedwith inner sleeve 200 by inserting stub section 110 into inner sleevecentral channel 210 at sleeve second end 204, thereby forming a stublens sub-assembly 250. In an example, an adhesive material 222 can beused to secure stub section 110 in central channel 210. When stub lenselement 100 is engaged with inner sleeve 200, the stub lens element axisA1 is substantially co-axial with inner sleeve axis A2. The stub lenssub-assembly 250 is thus configured to operably support optical fiberend 324 and stub lens element 100 in a cooperative optical relationship.

FIG. 6C is similar to FIG. 6B and shows an example wherein inner sleeve200 includes a slot 220 formed in inner sleeve outer surface 206 thatleads to central channel 210. FIG. 6D is similar to FIG. 6C and showsadhesive material 222 disposed in slot 220. Adhesive material 222 isintroduced into slot 220 and contacts stub section 110 of stub lenselement 100. This serves to secure (fix) the stub section to innersleeve 200, and providing an alternative to adding the adhesive materialto central channel 210 from one of its ends. Once adhesive material 222hardens, it can be ground, polished or otherwise processed to make itsouter surface conform to outer surface 206 of inner sleeve 200. The slot220 may be formed in inner sleeve 200 by laser beam LB or by mechanicalmeans, e.g., cutting or grinding.

As discussed below, it may be desirable to introduce adhesive material222 between stub lens element 100 and an optical fiber ferrule,introduced and discussed below. If channel 210 of inner sleeve 200 doesnot have a means for air to escape, then inserting adhesive material 222into the channel can be problematic. So slot 220 can serve theadditional function of providing a means for air to escape from channel210 during the fabrication process.

FIG. 7A is similar to FIG. 6B and shows stub lens sub-assembly 250 alongwith an optical fiber ferrule (“ferrule”) 300, and FIG. 7B is a close-upview of ferrule 300. The ferrule 300 has a central axis A3, first andsecond ends 302 and 304, an outer surface 306, and a central bore 310that runs along the central axis and that is open at the first andsecond ends. The central bore 310 is sized to fit into channel 210 ofinner sleeve 200. The ferrule 300 can be made of any rigid material,with glass, plastic and metal being some exemplary materials. In anexample, ferrule 300 comprises a section of precision capillary tubing.An example diameter of central bore 310 is about 128 microns, and anexample outer diameter of ferrule 300 is about 500 microns.

In an example, ferrule end 304 is angled at an angle φ relative tocentral axis A3. The central bore 310 of ferrule 300 is sized toaccommodate an optical fiber 320, which in an example is a single-modeoptical fiber. The 3ptical fiber 320 includes end 324, which residessubstantially at angled ferrule end 304. In the example where ferruleend 304 is angled, optical fiber end 324 can also be angled at the sameangle φ as the ferrule end. This can be accomplished by insertingoptical fiber 320 into ferrule 300 when it has a non-angled end 304, andthen forming the angled ferrule end 304 by a cutting and polishingprocess that serves also to cut and polish optical fiber end 324.

FIG. 7C shows ferrule 300, with optical fiber 320 secured therein,engaged with central channel 210 of inner sleeve 200 at inner sleeve end202, so that axes A1, A2 and A3 are all substantially co-axial. Theangled ferrule end 304 and angled end 14 of stub section 110 define agap 210G within central channel 210 between the respective angled ends.In an example, gap 210G can be filled with the aforementioned adhesivematerial 222 (not shown), e.g., in the form of an index-matching epoxy,to further reduce the back reflections and reduce the sensitivity of therotational alignment of opposing angled ends. The combination of stublens sub-assembly 250, ferrule 300 and optical fiber 320 form a stublens assembly 350. The stub lens assembly 350 has an object distance OD,which is defined as the axial distance between optical fiber end 324 andlens surface 42 of lens 40. In an example, object distance OD is in therange 0.5 mm≦OD≦5 mm, and in a more specific example is 1 mm≦OD≦3 mm.

With continuing reference to FIG. 7C, in an example, during thefabrication of stub lens assembly 350, one of the fabrication stepsincludes measuring the image MFD_(IM). This can be accomplished using,for example, a photodetector PD in the form of a beam-scanning apparatusor a digital camera. A light source LS is optically connected to an end323 of optical fiber 320. The photodetector PD is used to measure thesize of image spot 652 as formed by light 650 emanating from opticalfiber end 324 and being focused by stub lens element 100 at theanticipated working distance WD. The axial position of at least one offerrule 300 and stub lens element 100 can be adjusted until the objectdistance OD that minimizes the image MDF_(IM) is determined.

In an example, photodetector PD generates an electrical signal S1 thatis representative of the detected image MFD_(IM), and this electricalsignal is analyzed (e.g., via a computer CU operably connected tophotodetector PD) to assess the optimum object distance OD. Once theoptimum object distance OD is established, then ferrule 300 and stublens element 100 are fixed in place within inner sleeve 200 using, e.g.,adhesive material 222, which can be a UV-curable epoxy. In one example,stub lens element 100 is fixed relative to inner sleeve 200 prior to theimage MFD_(IM) measurement, and only the axial position of ferrule 300is adjusted. In an example fabrication step, gap 210G can be filled withthe aforementioned index-matching material, e.g., UV-curable adhesivematerial 222, through slot 220 (see FIGS. 7A and 7C).

In an example embodiment, stub lens assembly 350 is operably supportedby a support member. FIG. 8A is a cross-sectional view that shows stublens assembly 350 and a light-deflecting member 500 having an axis A5and arranged relative to a support member 398 in the form of an outersleeve 400 in the process of forming a probe optical assembly 450, asshown in FIG. 8B. The support member 398 is configured to operablysupport stub lens sub-assembly 350 and light-deflecting member 500 in acooperative optical relationship that defines folded optical path OP.

The light-deflecting member 500 is shown and discussed hereinbelow as aprism by way of illustration. In an alternate example, light-deflectingmember 500 comprises a mirror. The outer sleeve 400 has a central axisA4, first and second ends 402 and 404, an outer surface 406, and aninterior 410 that runs along the central axis and that is open at thefirst and second ends. The interior 410 is configured to accommodate atend 402 stub lens assembly 350 and at end 404 light-deflecting member500. In an example, outer sleeve 400 includes a retaining feature 412disposed within interior 410 at end 402, with the retaining featureconfigured to retain inner sleeve 200 of stub lens assembly 350. Theouter sleeve 400 can be made of any rigid material, with glass, plasticand metal being exemplary materials. In an example, outer sleeve 400comprises a section of precision capillary tube.

With continuing reference to FIG. 8A, light-deflecting member 500includes a cylindrically curved front surface 502, a planar angledsurface 503 that defines a total-internal-reflection (TIR) mirror 503M,and a planar bottom surface 504. The light-deflecting member centralaxis A5 is folded by TIR mirror 503M. The angle of deflection α can bein the range between 90 and 100 degrees.

The light-deflecting member 500 is shown along with a retaining feature512 that serves to retain the light-deflecting member in interior 410 atend 404 of outer sleeve 400 when the light-deflecting member and theouter sleeve are operably engaged. In an example, retaining feature 512is simply adhesive material 222.

FIG. 8B shows stub lens assembly 350 and light-deflecting member 500operably engaged with outer sleeve 400 at respective ends 402 and 404,thereby forming the aforementioned probe optical assembly 450. The probeoptical assembly 450 includes an optical path OP that begins fromoptical fiber end 324 and that generally follows the substantiallyco-axial axes A1 through A5. In an example, optical fiber end 324defines an object plane OBP and working distance WD defines the distancewhere light-deflecting-member axis A5 intersects axis A4 to an imageplane IMP where the smallest image spot 652 is formed. The optical pathOP thus comprises the path over which light 650 travels from objectplane OBP to image plane IMP.

OCT Probe

FIG. 9A is similar to FIG. 8B and shows an example of an OCT probe(“probe”) 600 that includes a long (e.g., several meters long)transparent jacket 610 into which probe optical assembly 450 and opticalfiber 320 are inserted. An example jacket 610 has a cylindrical bodyportion 620 that defines an interior 624. In an example, jacket 610comprises a long polymer tube having a rounded distal end 616. Thecylindrical body portion 620 has a cylindrically curved outer surface626. In an example, jacket 610 has a diameter D3 in the range 1 mm≦D3≦2mm.

The jacket 610 is configured to contain probe optical assembly 450 ininterior 624. FIG. 9A also shows an example where jacket 610 includes aproximal end 614 at which an optical fiber cable 326 that carriesoptical fiber 320 is operably connected to the jacket.

FIG. 9B is a close-up view of the probe optical assembly 450 containedwithin interior 624 of jacket 610 of probe 600 and shows light 650 andscattered light traversing optical path OP in opposite directions. Thelight 650 originates from light source LS, which is optically coupled toend 323 of optical fiber 320. In an example, light 650 from light sourceLS has a wavelength of about 1.3 um. The use of a single-mode opticalfiber provides the necessary spatial coherence for OCT applications.

With reference to FIG. 9A and FIG. 9B, light 650 from light source LSinitially travels down optical fiber 320 as guided light. This guidedlight 650 exits optical fiber end 324 at or near ferrule end 304 anddiverges as it begins traveling over optical path OP. This divergentlight then passes through gap 210G and enters proximal end 14 of stubsection 110 of stub lens element 100. The divergent light 650 thentravels through stub section 110 to lens 40, where it exits the lens atlens surface 42 and passes to light-deflecting member 500. Note thatlens surface 42 has positive optical power and so acts to converge light650. The now convergent light 650 enters light-deflecting member 500 atcurved surface 502, and is then totally internally reflected at TIRmirror 503M within the light-deflecting member. This reflection directsconvergent light 650 to continue traveling along axis A5 and to exitlight-deflecting member 500 at bottom surface 504. The light 650 thenpasses through cylindrical body portion 620 of transparent jacket 610that resides adjacent light-deflecting member bottom surface 504 andexits probe 600. Thus, optical path OP passes through transparent jacket610.

It is noted here that cylindrical curvature of cylindrical body portion620 of jacket 610 acts as a cylindrical lens surface and so has firstoptical power in one direction. Accordingly, in an example,cylindrically curved front surface 502 of light-deflecting member 500 isconfigured to have second optical power that compensates for the firstoptical power. In an example, this compensation can be provided asnegative optical power (i.e., a 1D concave surface) on surface 502 inthe same plane of curvature as cylindrical body portion 620 or aspositive optical power (i.e., a 1D convex surface) in the plane ofcurvature orthogonal to the cylindrical body portion. Thus, in one case,the same negative (diverging) optical effect is introduced in both axes,while in another case, the positive (converging) optical effectcompensates for the diverging effect of the curved outer surface 626 ofjacket 610. Surface 502 of light-deflecting member 500 can be madecurved using standard micro-polishing and micro-finishing techniques.

The light 650 that exits probe 600 then travels to a sample 700, whichresides adjacent the probe as shown in FIG. 9A. The sample 700 has abody (volume) 701 that defines a sample surface 702. The convergentlight 650 is substantially brought to a focus at working distance WD byvirtue of lens surface 42 of stub lens element 100 having theaforementioned positive optical power. The focused light 650 forms imagespot 652, which has associated image MFD_(IM), as illustrated in theclose-up inset view of the image spot.

A portion 650S of light 650 incident upon sample 700 is scattered backfrom sample surface 702 or volume 701 into probe optical assembly 450through the cylindrical body portion 620 of transparent jacket 610. Thisscattered light 650S then travels back through probe optical assembly450 over optical path OP but in the reverse direction to that ofincident light 650. The scattered light 650 is then diverted upstreamfrom optical fiber 320 by a fiber coupler FC to travel in anotheroptical fiber section 318 (FIG. 8B) to be interfered with referencelight (not shown). The interfered light is then detected and processedaccording to conventional OCT procedures.

The stub lens element 100 serves to receive light 650 emitted fromoptical fiber end 324 and form a high-quality Gaussian beam. In anexample, stub lens element 100 and light-deflecting member 500 areconfigured to meet the requirements for the image mode-field diameter(MFD) and working distance WD for OCT applications. The angled opticalfiber end 324 and angled end 14 of stub section 110 serve to reduce backreflections [and thereby?] to improve the SNR. As discussed above, gap210G between angled ferrule end 324 and ferrule and angled end 14 ofstub section 110 can be filled with an index-matching material tofurther reduce back reflections as well as to reduce the sensitivity ofthe rotational alignment of the opposing angled ends that define thegap.

Design Considerations

FIG. 10 plots the object distance OD (horizontal axis) vs. the workingdistance WD (left vertical axis, solid-line curve) and the mode fielddiameter MFD (right vertical axis, dotted-line curve) in connection withdesigning an example stub lens element 100. All dimensions are inmicrons. A Gaussian beam for light 650 was used, along with a radius ofcurvature of 0.75 mm for lens surface 42, and silica as the opticalmaterial. The wavelength of light 650 was 1.3 microns, at which silicahas a refractive index n of about 1.45.

Based on the plot of FIG.10, in order to have a working distance WD ofabout 13.5 mm, the object distance OD needs to be about 2890 microns.The corresponding image MFD_(IM) is about 60 microns.

The plot of FIG. 10 can also be used to determine the tolerances neededfor this design to control working distance WD to within certain limits.As can be seen by a circle C1 provided on the solid-line curve, objectdistance OD needs to be controlled to better than about 10 microns inorder to control working distance WD to better than 500 microns.Likewise, with reference to a circle C2 on the dotted-line curve,controlling object distance OD to within 10 microns controls mode fielddiameter MFD to within about 25 microns. Like plots can be made for thetolerances on the radius of curvature of lens surface 42. These kinds oftolerance assessments indicate the need for very tight control ofworking distance WD if good OCT imaging is to be obtained.

In OCT applications, the transverse imaging resolution depends on imageMFD_(IM) of image spot 652 formed at working distance WD. A smallerimage spot 652 with the same working distance WD is thus desired toachieve higher imaging resolution.

FIG. 11 is similar to FIG. 10 and plots the image MFD_(IM) (microns)versus the working distance WD (microns) for the case of a single-modeoptical fiber 320, but where the input fiber MFD_(F) is changed from 10microns to 7 microns. The solid line and dashed line curves representtwo different glass types for stub lens element 100, namely, PYREX andsilica, which has a lower index than PYREX. The dotted line indicatesthe results with a smaller mode field fiber. The curves plotted in FIG.11 indicate that the smaller fiber MFDF leads to a smaller imageMFD_(IM) at the same working distance WD. Similarly, a smallerrefractive index n for stub lens element 100 (for example, silica vs.PYREX) leads to a smaller image MFD_(IM).

FIG. 12 is similar to FIG. 7B and illustrates an example modification ofoptical fiber 320 at optical fiber end 324. In the example, rather thanusing an optical fiber 320 having a smaller core diameter, a lens 325 isformed on (e.g., via re-shaping via acid etching or melting) or isotherwise added directly to optical fiber end 324. The lens 325 can haveany one of a variety of surface shapes, including spherical andaspherical. Example aspherical surface shapes include parabolic shapes,hyperbolic shapes, biconic shapes, and the like. The shape of lens 325is limited only by current optical fiber lens-forming techniques.

The lens 325 is configured to reduce fiber MFD_(F), which in turnreduces image MFD_(IM). Example specifications for image MFD_(IM),working distance WD, and the M² parameter for light 650 are about 80microns, about 13.5 mm to 15 mm and less than 1.3, respectively.Embodiments of probe 600 fabricated using the components, assemblies andmethods as described herein can readily meet these specifications.

FIG. 13A through FIG. 13C illustrate an example method of forming afiber pigtail lens assembly 800 that can serve as a more compact versionof the previously described stub lens assembly 350. With reference firstto FIG. 13A, optical fiber 320 is spliced at optical fiber end 324 toend 14 of rod 10. The optical fiber 320 has a core 322, which in anexample is comprised of silica or doped silica. In an example, rod 10 ismade of silica so that optical fiber core 322 and the rod aresubstantially index matched. Splicing optical fiber 320 to rod 10 formsa contiguous fiber pigtail structure 348 that is further processed toform fiber pigtail lens assembly 800. The general process for formingthis monolithic fiber pigtail structure 348 is described in U.S. Pat.Nos. 7,228,033 B2, 7,258,495 B1 and 6,904,197 B2, which are incorporatedby reference herein.

With reference now to FIG. 13B, rod distal end portion 17 is processedto have a tapered shape and so that rod 10 has a select length to withinabout +/−20 microns. By controlling the shape of rod distal end portion17, the subsequent lens 40 can be made to have a select configuration.

With reference now to FIG. 13C, monolithic fiber pigtail structure 348of FIG. 13B is further processed using for example the thermal methodsdescribed above so that rod distal end portion 17 becomes bulbous andforms lens 40 with lens surface 42 having a nominal radius of curvatureR2. Thus, the resulting fiber pigtail lens assembly 800 includes a stublens element 100 that includes stub section 110 spliced at end 14 tooptical fiber 320. In fiber pigtail lens assembly 800, the objectdistance OD is now essentially the axial distance or length L of thenewly formed stub lens element 100, wherein L is the distance fromproximal end 14 of stub section 110 to the apex of lens surface 42 oflens 40. In an example, length L is in the range 0.5 mm to 5.0 mm.

FIG. 13D is similar to FIG. 13C and shows the fiber pigtail assembly 800operably engaged with ferrule 300 so that lens 40 is adjacent ferruleend 304. Adhesive material 222 is included within central bore 310 andis used to fix stub section 110 and the spliced-end portion of opticalfiber 320 within the ferrule channel.

FIG. 13E is similar to FIG. 13D and shows an example embodiment wherelens 40 has been reduced in size by polishing, turning, grinding or likemanner. This makes fiber pigtail assembly 800 smaller in the lateraldimension, which allows it to be used in different configurations wherea wider bulbous lens 40 might prove problematic. For example, withreference to FIG. 13F, the fiber pigtail assembly 800 and ferrule 300are shown operably supported by support member 398 in the form of atransparent support substrate 820 having an upper surface 828. In anexample, support substrate 820 supports an example light-deflectingmember 500 in the form of a prism atop upper surface 828 adjacent oneend of the substrate. The support substrate 820 also supports fiberpigtail assembly 800 and ferrule 300 on surface 828 near the other endof the support substrate. In an example, support substrate 820 has athickness of about 190 microns.

In the example shown, light-deflecting member 500 now has a planarlight-deflecting member front surface 502, along with the aforementionedangled surface 503 that defines a TIR mirror 503M, and bottom surface504, which now resides adjacent the substrate upper surface 828. Thefiber pigtail assembly 800 is disposed on upper surface 828 and in anexample is secured thereto, e.g., with adhesive material 222. The fiberpigtail assembly 800 is arranged so that lens surface 42 of lens 40confronts planar light-deflecting-member surface 502. Thelight-deflecting member TIR mirror 503M serves to fold axis A1 so thatoptical path OP passes through support substrate 820 at the locationadjacent light-deflecting member bottom surface 504.

In an example, light-deflecting member 500 can be formed by providing ablank (also called a preform) having a triangular cross-section and thatcan include a corresponding surface that has either a convex or concavecurvature, depending on how the compensation for curved jacket 610 is tobe carried out via the subsequently formed light-deflecting member. Theblank is then drawn into rods using standard glass drawing techniques,wherein the rods have the same cross-sectional shape as the blank.

This light-deflecting member fabrication method requires shaping oneblank from which hundreds of meters of light-deflecting-member rods canthen be drawn. Centimeter lengths of the light-deflecting-member rodscan be mounted on support substrate 820 and then diced into individuallight-deflecting members and substrates such as shown in FIG. 13F

In an example, the blank is formed so that light-deflecting-membersurface 502 has the appropriate curvature. Moreover, in an example,light-deflecting-member surface 502 can have an amount of tilt relativeto light-deflecting member axis A5 that is capable of reducing backreflections. For example, for most anticipated OCT applications, a tiltof about 2 degrees is sufficient for reducing back reflections to as lowas −50 dB to −60 dB.

FIG. 14 is similar to FIG. 8B and illustrates an example embodiment ofprobe optical assembly 450 that employs fiber pigtail lens assembly 800in place of the aforementioned stub lens assembly 350. The fiber pigtaillens assembly 800 is shown being held in place within outer sleeve 400by retaining feature 412. The use of fiber pigtail lens assembly 800simplifies the design and assembly of probe optical assembly 450 andalso eliminates gap 210G, which was present in stub lens assembly 350described above. The configuration of fusion-spliced fiber pigtail lensassembly 800 reduces the amount of back reflection to an acceptablelevel without the need for angled facets. This contributes to pigtaillens assembly 800 having robust performance while also having arelatively low assembly cost. FIG. 14 also shows an example oflight-deflecting member 500 operably engaged at end 404 of outer sleeve400. In an example, light-deflecting member 500 can be molded orembossed to sleeve 400 using polymers or UV curable epoxies.

The fiber pigtail lens assembly 800 is relatively tolerant to processvariations. The underlying reason for this has to do with the fact thatthe amount of optical material needed to form lens 40 is proportional tothe cube of the lens radius R2, whereas the amount of material containedin the cylindrical stub section 110 is proportional to the square of therod radius R1, wherein R1=(D1)/2. For OCT imaging, an example lensradius R2 for lens 40 of fiber pigtail lens assembly 800 is in the rangeabout 750 microns to about 800 microns. In an example, rod 10 from whichlens 40 is formed has a diameter D1 in the range of about 350 microns toabout 500 microns.

A variation in the length L of stub lens element 100 is dictated by theshortening of rod 10 during the formation of lens 40. FIG. 15 plots therelationship between the stub lens element length L (mm) and thediameter D2 (mm) of lens 40 of stub lens element 100. The totalvariation in length L is ostensibly determined by the accuracy of themechanism used to feed rod 10 into heat source 20 during the lensformation process (see FIG. 1). Even with a change in length ΔL of 50microns, the corresponding change in the lens diameter ΔD2 is only about2.5 microns. This amount of change in the diameter D2 of lens 40 doesnot lead to a significant change in the focusing characteristics of thelens, so the working distance WD and image MFD_(IM) remain substantiallyunchanged.

FIG. 16A is a cross-sectional view of another example embodiment of stublens assembly 350 that includes fiber pigtail lens assembly 800, whereinits fused stub lens element is denoted as 100A (with lens 40A, lenssurface 42A, etc.), as used in combination with a second stub lenselement, which is denoted as 100B (with lens 40B, lens surface 42B,etc.). The support member 398 in the form of inner sleeve 200 operablysupports ferrule 300 at first end 202 and operably supports stub lenselement 100B at second end 204.

This configuration of stub lens assembly 350 now has two opticalsurfaces with optical power, namely stub lens surfaces 42A and 42B. Thestub lens surfaces 42A and 42B are arranged in stub lens assembly 350 sothat they are confronting. The fiber MFD_(F) associated with fiberpigtail lens assembly 800 in this example can be made relatively small.This in turn allows for optical fiber 320 to be a conventional opticalfiber, such as SMF-28® optical fiber, which is available from Corning,Inc., Corning, N.Y., and which has a core diameter of nominally 10microns.

Another advantage is that the amount of back scattering of light 650 isrelatively low by virtue of the pigtail configuration of fiber pigtaillens assembly 800. Also, the two lenses 40A and 40B can be configured sothat light 650 is substantially collimated as it travels from lenssurface 42A to lens surface 42B, as illustrated in FIG. 16A. This canserve to reduce any beam distortions and also to reduce the diameterrequirements for lens 40B of stub lens element 100B.

FIG. 16B is similar to FIG. 16A and illustrates an example embodiment ofstub lens assembly 350 wherein outer sleeve 200 is replaced with supportsubstrate 820. The support substrate 820 can be made of a rigid materialsuch as glass, plastic, metal and the like.

FIG. 17 is similar to FIG. 16B and illustrates another exampleembodiment of stub lens assembly 350 wherein support substrate 820 ismade of a transparent material. In an example, support substrate 820 isformed as a unitary molded piece that includes first and second ends 824and 826, and a recess 830 formed in upper surface 828. The ferrule 300with fiber pigtail lens assembly 800 engaged therewith is disposed onupper surface 828 of support substrate 820 adjacent end 824. Likewise,stub lens element 100B is disposed on upper surface 828 of supportsubstrate 820 adjacent end 826, with the stub lens surface 42B inopposition to stub lens surface 42A. Stub lens element 100B has anangled distal end 14B that defines a TIR mirror 14BM.

The stub lens elements 100A and 100B are aligned (i.e., their respectiveaxes A1A and A1B are made co-linear) using for example theaforementioned method of monitoring of the image MFD_(IM) (see FIG. 7C).Once so aligned, they are fixed in position. In an example, stub lenselement 100B can be secured to support substrate 820 by an adhesivematerial 222 introduced into recess 830, where a portion of lens 40Bresides. Note that the portion of stub section 110B that includes TIRmirror 14BM serves essentially the same function as the aforementionedseparate light-deflecting member 500. The fiber pigtail lens assembly800 can be axially adjusted within ferrule 300 prior to being fixed inplace.

FIG. 18 is similar to FIG. 17 and illustrates an embodiment wherein thesupport member 398 comprises a transparent monolithic structure 850 thatincludes ends 854 and 856, and a planar upper surface portion 858adjacent end 854. The monolithic structure 850 also includes stub lenselement portion 100B adjacent end 856, with the stub lens elementportion including angled end 14B and TIR mirror 14BM. In an example,planar upper surface portion 858 includes at least one alignment feature860 that facilitates alignment of ferrule 300 and fiber pigtail lensassembly 800 supported thereby with the stub lens element portion 100B.An example alignment feature 860 is a groove (e.g., a V-groove) thataccommodates a corresponding (e.g., complimentary) alignment feature 360of ferrule 300.

The monolithic structure 850 can be formed, for example, by molding apolymer material, thereby providing for low-cost mass production thatcan employ reusable molds. The configurations of stub lens assembly 350of FIG. 18 has the advantage that the beam dimension of light 650 issubstantially larger compared to the single mode fiber mode-fielddiameter before it is incident on lens surface 42B. This substantiallyreduces the light intensity on the lens surfaces so that they cantolerate much higher power levels without degradation, especially whenmonolithic structure 850 comprises a polymer material.

FIG. 19 is a plot of the length L (microns) (horizontal axis) versus theimage MFD_(IM) (microns)(left-hand vertical axis) and working distanceWD (microns)(right-hand vertical axis) as defined as the beam-waistlocation, for an example stub lens element 100 suitable for use in fusedfiber pigtail lens assembly 800. The curve with the circles correspondsto image MFD_(IM) and the curve with the squares corresponds to workingdistance WD. The plot of FIG. 19 is based on lens 40 having a radiusR2=150 microns and optical fiber 320 having a fiber MFD_(F) of about 10microns. The plot shows that fiber pigtail lens assembly 800 can have animage MFD_(IM) of about 6.5 microns for a length L of 1,200 microns (1.2mm).

FIG. 20 is a side view of an example fiber pigtail lens assembly 800wherein lens 40 includes an angled surface (facet) 43 that defines a TIRmirror 43M that serves to fold axis A1 and direct it through a portionof lens surface 42. The facet 43 can also include a curvature tocompensate for the defocusing effect of curved outer surface 626 ofjacket 610.

FIG. 21 is another embodiment of the fiber pigtail assembly 800 assemblysimilar to that shown in FIG. 20, but where optical fiber 320 is notfusion spliced to lens 40. Rather, optical fiber end 324 is spaced apartfrom lens 40 and is in optical communication therewith throughindex-matching material 222, e.g., UV epoxy. The optical fiber 320 isshown being supported in ferrule 300, which in turn is supported ininner sleeve 200. As with lens 40 of FIG. 20, lens 40 of FIG. 21performs both the beam bending at lens surface 42 and the internalreflection at angled surface (facet) 43. In the example of FIG. 21, lens40 is formed as a single element fabricated from a hemispherical orbiconic ball lens made of a glass or a polymer material. With polymermaterials, the fabrication of biconic lens or shaped stub lens isgenerally easier and can be more readily mass produced, e.g., via amolding process.

Although the embodiments herein have been described with reference toparticular aspects and features, it is to be understood that theseembodiments are merely illustrative of desired principles andapplications. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the appended claims.

What is claimed is:
 1. A probe optical assembly for a probe for anoptical coherence tomography (OCT) system, comprising in order along anaxis: an optical fiber having an end that defines an object plane; astub lens element having a stub section with a proximal end that residesadjacent the optical fiber end, the stub section being formed integralwith a lens having a proximal end that includes a lens surface; alight-deflecting member arranged adjacent and spaced apart from the lenssurface of the stub lens element, the light-deflecting element having anaxis that defines a working distance WD to an image plane; and whereinthe optical fiber end, the stub lens element and the light-deflectingmember are arranged in a cooperative optical relationship to define anoptical path between the object and image planes that is folded by thelight-deflecting member.
 2. The probe optical assembly of claim 1,wherein the optical fiber and stub lens are supported in a cooperativeoptical relationship by a sleeve having a central channel in which thestub section resides.
 3. The probe optical assembly of claim 1, whereinthe optical fiber is supported by an optical fiber ferrule, which inturn at least partially resides within the central channel of thesleeve.
 4. The probe optical assembly of claim 1, wherein thelight-deflecting member comprises a prism having atotal-internal-reflection surface.
 5. The probe optical assembly ofclaim 1, wherein the optical fiber end and the proximal end of the stubsection of the stub lens element have respective angles relative to theaxis.
 6. The probe optical assembly of claim 1, wherein the opticalfiber end abuts the proximal end of the stub section.
 7. The probeoptical assembly of claim 1, wherein the light-deflecting memberincludes at least one surface having optical power.
 8. The probe opticalassembly of claim 1, wherein the optical fiber comprises a single-modeoptical fiber.
 9. The probe optical assembly of claim 1, wherein lightemitted from the optical fiber end and traveling over the optical pathforms an image spot at the image plane having an image mode fielddiameter MDF_(IM) in the range 15 microns≦MDF_(IM)≦100 microns.
 10. Theprobe optical assembly of claim 1, wherein the working distance WD is inthe range 5 mm≦WD≦15 mm.
 11. The probe optical assembly of claim 1,wherein the stub lens element and light-deflecting member are each partof a monolithic and transparent support member.
 12. The probe opticalassembly of claim 1, wherein the stub lens element and light-deflectingmember are supported by a transparent support substrate.
 13. A probe foran optical coherence tomography system, comprising: the probe opticalassembly of claim 1; and a transparent jacket that contains the probeoptical assembly and through which the optical path passes.
 14. Theprobe of claim 13, wherein the transparent jacket has a diameter D3 inthe range 1.0 mm≦D3≦2.0 mm.
 15. The probe of claim 13, where thetransparent jacket comprises polymer tubing.
 16. A probe opticalassembly that defines an optical path and that is suitable for use informing an optical coherence tomography (OCT) probe, comprising: a stublens sub-assembly comprising i) an optical fiber having a first end anda second end, and ii) a stub lens element having a central axis, a lenswith a lens surface that defines a distal end, and a stub sectionintegrally formed with the lens and having a proximal end, the stub lenssub-assembly being configured so that the optical fiber end is inoptical communication with the stub lens proximal end over the opticalpath; a support member configured to operably support the stub lenssub-assembly so that the lens of the stub lens element resides withinthe interior; and a light-deflecting member having a second axis andoperably supported by the support member so that the first and secondaxes are generally coaxial, and wherein a portion of the second axis isfolded to define a fold in the optical path.
 17. The probe opticalassembly of claim 16, wherein the light-deflecting member includes atleast one surface having optical power.
 18. The probe optical assemblyof claim 16, wherein the optical path includes an object distance ODbetween the optical fiber end and the lens surface, and wherein theobject distance OD is in the range of 1.0 mm to 3.0 mm.
 19. The probeoptical assembly of claim 16, wherein light emanating from the opticalfiber end travels over the optical path and forms an image spot havingan image mode field diameter in the range of 15 microns to 100 microns.20. An optical coherence tomography (OCT) probe, comprising: The probeoptical assembly of claim 16; and a transparent jacket having aninterior that contains the probe optical assembly.